Why the Sun's Corona is 300 Times Hotter Than Its Surface: Nanoflares (VIDEO)

Astronomers have caught a glimpse into the very heart of a solar storm. They've taken a close at a space weather storm that engulfed our planet on Jan 21, 2005 after a coronal mass ejection (CME) burst off of the sun and headed toward Earth. Scientists have investigated the solar system's prehistoric phase and the events that led to the birth of the sun. NASA's Solar Dynamics Observatory captured this image of what the sun looked like on April 23, 2013, at 1:30 p.m. EDT when the EUNIS mission launched. (Photo : NASA/SDO)

You'd think that the sun's surface would be hotter than its outer atmosphere, but that's not the case. In fact, it's a phenomenon that has puzzled scientists for decades. Now, they may have the answer; new observations reveal that it may have something to do with nanoflares.

Nanoflares are a constant peppering of impulsive bursts of heating, none of which can technically be detected. Current theory states that these tiny flares could be powering the heating in the sun's outer atmosphere. Certainly, something has to be powering it. While the sun's surface is a whopping 3,000 Kelvins, the corona temperatures are almost 300 times as hot.

"That's a bit of a puzzle," said Jeff Brosius, space scientist at NASA's Goddard Space Flight Center, in a news release. "Things usually get cooler farther away from a hot source. When you're roasting a marshmallow you move it closer to the fire to cook it, not farther away."

Now scientists have used data from the EUNIS mission in order to learn a bit more about the sun's unusual pattern of heating. Standing for Extreme Ultraviolet Normal Incidence Spectrograph, the EUNIS mission gathers a new snapshot of data every 1.3 seconds in order to track the properties of material over a wide range of temperatures in the solar atmosphere. It was tuned into a range of wavelengths useful for spotting temperatures of 10 million Kelvin, which are temperatures that are a signature of nanoflares.

So what did they find? It turns out EUNIS was able to pick up a wavelength of light corresponding to that 10 million degree material.

"The fact that we were able to resolve this emission line so clearly from its neighbors is what makes spectroscopists like me stay awake at night with excitement," said Brosius. "This weak line observed over such a large fraction of an active region really gives us the strongest evidence yet for the presence of nanoflares."

The findings reveal a bit more about why the sun's corona is so much hotter than its surface. It's very possible, with this new data as evidence, that nanoflares are to blame.